Spatial distribution of irrigation water quota of highland barley in Tibet region

Abstract: The objective of this study was to estimate the irrigation water quota and their spatial distribution of highland Barley in Tibet. Tibetan plateau has the characters of high altitude, low air pressure, vast geographic, and has significant differences on climate spatial distribution. Until now, Tibet has very few measured irrigation and drainage experiment data of crops. This paper tried to combine theoretical calculation and survey data together to find a method to calculate the irrigation water quota and obtain a contour map under different irrigation frequency in convenient for project design. Four represent highland barley planting sites in each of four agricultural growth partitions of Tibet were selected to get information on irrigation, cultivation, soil conditions and meteorological characteristics, then 28 meteorological stations' long series of climate data were gathered. To calculate the accurate irrigation water quota of Tibet highland barley, water balance method was applied to calculate daily water balance processes during the growth period. In this process, precipitation, effective precipitation, root zone soil moisture, evapotranspiration, percolation, drainage and so on factors were used. Root zone's soil water was determined by scheming wetness depth and appropriate upper and lower soil moisture limit, and ETc(evapotranspiration) was determined by FAO. Kcini, Kcmid, Kcend were modified considering soil and crop evaporation separately by recommended dual crop coefficient. Kc of four typical sites were calculated, and then irrigation water quota from 1957 to 2009 were calculated by daily water balance in different hydrological years. By comparing the calculated results with surveyed irrigation data, four sites' calculated results were validated, and then the other 24 sites of the 4 partitions' irrigation water quota were also calculated. According to 28 sites' results, Kringing interpolation method was used to get the contour map of Tibet highland barley irrigation water quota in different hydrological years. Climate factors that may interpret irrigation water quota for highland barley were analyzed using Kringing method and contour maps were also obtained. Results showed, in general, from the northwest to the southeast, irrigation water quota decreased gradually. Highland barley irrigation water quotas in Tibetan decreased with precipitation and increased with temperature and ET0.